In optical waveguides, which for example, are used for optical data transmission, and cavities, which, for example, are used on laser resonators, the propagation of light is limited in at least two spatial directions. In this case, the wave guidance usually takes place by total reflection at the interface between an optically denser and an optically less dense medium. The light propagates in the optically denser medium in this case.
Recent scientific papers are concerned with the propagation of light in periodic dielectric lattice structures. The propagation of light in structures of this type can be described analogously to the propagation of electrons in a crystal. If the wavelength of the light is of the order of magnitude of the dimensions of the lattice, then a photonic band gap can form. The photonic band gap is a frequency range in which photons cannot propagate. This means that if light at a frequency which lies in the frequency range of the photonic band gap is radiated onto a structure of this type, then this light cannot propagate in the structure. Instead, it is reflected at the surface. This effect has been confirmed by experiments (see, for example, an article by E. Yablonovich, "Photonic Band Gaps and Localization", ed. C. M. Soukoulis, Plenum, New York, 1993, pages 207 to 234, or an article by U. Gruning et al., Appl. Phys. Lett., Vol. 66, No. 24, 1995, pages 3254 to 3256). This reflection is also referred to as a Bragg reflection at the dielectric lattice.
The experimental investigations were carried out on structures in which the lattice structure is realized as a layer structure having alternating layers with a different refractive index or from a nonmetallic material such as, for example, AlGaAs or GaAs or Si having pores arranged in a periodic grid pattern. In AlGaAs and GaAs, these pores are produced by reactive ion etching. In silicon, these pores have been produced by electrochemical etching.
On the basis of theoretical considerations and calculations, it has been proposed to utilize the effect of the Bragg reflection at the dielectric lattice for the purpose of realizing cavities and optical waveguides (see, for example, an article by R. Maede et al., J. Appl. Phys., Vol. 75, No. 9, 1994, page 4753). In this case, two regions made of a material having a photonic band gap are used for an optical waveguide. GaAs with a periodic hole structure has been proposed as a material for the photonic band gap. As the optical waveguide, the starting material, GaAs, without hole structures is arranged between the two regions. In this optical waveguide, light having a wavelength which corresponds to a frequency in the photonic band gap is guided in a plane by virtue of the fact that it cannot propagate into the material having the photonic band gap. In the plane perpendicular to this, the light is guided by total reflection at the interface between the optically denser GaAs and the surrounding, optically less dense atmosphere. In order to realize a cavity, material having a photonic band gap is provided for the purpose of limiting the propagation of the light in the third spatial direction.